PASADENA, Calif., Jan. 14 — NASA’s Spirit rover completed repositioning itself Wednesday and was ready to roll off its lander and onto the surface of Mars to begin its three-month journey of discovery, the space agency said.

Controllers planned to command Spirit early Thursday to roll down a ramp and come to a stop on the salmon-colored martian soil. The 10-foot trip was expected to take less than two minutes.

It was expected to be the riskiest step Spirit would take while on Mars. Scientists at NASA’s Jet Propulsion Laboratory hoped to learn between 4 a.m. and 5 a.m. ET Thursday whether the maneuver was a success.

After that, the space agency plans to keep Spirit parked for several days, taking measurements of soil and rocks around the rover, before they send it trundling off on a zigzagging path to look for evidence that the Red Planet was once wetter and hospitable to life.

On Wednesday, the rover finished the last of three turns atop its lander, rotating 115 degrees in order to line up its six wheels with the ramp.

The rover was actually supposed to use another ramp that would have taken it directly onto the surface of the planet. But the now-deflated air bags that cushioned the rover’s landing on Mars were blocking the way, requiring the pirouette.

Since landing Jan. 3, Spirit has shot panoramas of its surroundings that scientists are using to plot the rover’s course. Its nine cameras have snapped at least 3,900 pictures and transmitted them to Earth.

Spirit looks up, orbiters look down
During roll-off, NASA planned for Spirit to carry out coordinated scientific observations with a second NASA martian spacecraft. Spirit was to gaze skyward while the 2001 Mars Odyssey orbiter looked down on the site. A day later, Spirit will do the same when the European Mars Express satellite flies overhead.

The coordinated observations were designed to allow scientists to study the dynamics of the martian atmosphere.

Once Spirit sets off on its journey, it will roll toward a crater about 825 feet away. Later, it could strike out toward a cluster of hills nearly two miles away, or about five times farther than Spirit is expected to be able to travel.

The $820 million project also includes a second, identical rover named Opportunity. Spirit’s twin should land on the opposite side of the Red Planet on Jan. 24.